Note 8 - Stock-based Compensation - Summary of Restricted Common Stock Activity (Details) - $ / shares	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Restricted Stock [Member]
Outstanding, Shares (in shares)	917,533	977,547	578,894
Outstanding, Weighted average grant date fair value (in dollars per share)	$ 16.84	$ 15.45	$ 13.14
Granted, Shares (in shares)	731,374	359,481	751,463
Granted, Weighted average grant date fair value (in dollars per share)	$ 19.73	$ 18.92	$ 16.07
Vested, Shares (in shares)	(613,179)	(333,865)	(352,810)
Vested, Weighted average grant date fair value (in dollars per share)	$ 15.48	$ 15.35	$ 12.98
Forfeited, Shares (in shares)	0	(85,630)	0
Forfeited, Weighted average grant date fair value (in dollars per share)	$ 0	$ 15.53	$ 0
Outstanding, Shares (in shares)	1,035,728	917,533	977,547
Outstanding, Weighted average grant date fair value (in dollars per share)	$ 19.69	$ 16.84	$ 15.45
Restricted Stock [Member] \| Common Class A [Member]
Outstanding, Shares (in shares)	480,042	449,284	407,786
Outstanding, Weighted average grant date fair value (in dollars per share)	$ 16.10	$ 13.55	$ 11.82
Granted, Shares (in shares)	488,918	166,814	199,810
Granted, Weighted average grant date fair value (in dollars per share)	$ 18.66	$ 19.87	$ 15.36
Vested, Shares (in shares)	(248,539)	(136,056)	(158,312)
Vested, Weighted average grant date fair value (in dollars per share)	$ 15.00	$ 12.32	$ 11.38
Outstanding, Shares (in shares)	720,421	480,042	449,284
Outstanding, Weighted average grant date fair value (in dollars per share)	$ 18.22	$ 16.10	$ 13.55
Restricted Stock Units (RSUs) [Member]
Outstanding, Shares (in shares)	90,184	398,000	0
Outstanding, Weighted average grant date fair value (in dollars per share)	$ 18.92	$ 18.21	$ 0
Granted, Shares (in shares)	95,115	93,184	398,000
Granted, Weighted average grant date fair value (in dollars per share)	$ 19.05	$ 18.77	$ 18.21
Vested, Shares (in shares)	(60,052)	(374,500)	0
Vested, Weighted average grant date fair value (in dollars per share)	$ 18.92	$ 18.18	$ 0
Forfeited, Shares (in shares)	0	(26,500)	0
Forfeited, Weighted average grant date fair value (in dollars per share)	$ 0	$ 18.21	$ 0
Outstanding, Shares (in shares)	125,247	90,184	398,000
Outstanding, Weighted average grant date fair value (in dollars per share)	$ 19.02	$ 18.92	$ 18.21

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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-Name Accounting Standards Codification
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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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